1. Field of the Invention
The present invention relates to a method for manufacturing a composite film including a polarizing film and a support film, and a composite film obtained by the manufacturing method.
2. Description of the Related Art
A polarizing film is generally manufactured by stretching a film on which a dichroic material is adsorbed. A stretching direction of the polarizing film is generally a longitudinal direction or a width direction of the film due to restrictions of a stretching apparatus. When the film is stretched in a longitudinal direction, the absorption axis is directed in the longitudinal direction, whereas when stretched in a width direction, the absorption axis is directed in the width direction. In either case, the absorption axis is parallel to or perpendicular to the width direction of the film, and cannot be oblique to the width direction. The phrase “the absorption axis is oblique to the width direction” means that the absorption axis is neither parallel to nor perpendicular to the width direction.
However, there may be cases where a polarizing film having an absorption axis oblique to the width direction is higher in the rate of utilization. Therefore, in order to attain the polarizing film having an absorption axis oblique to the width direction, there is known a manufacturing method of obliquely stretching the film by use of a special tenter stretching apparatus (for example, Japanese Unexamined Patent Publication No. 2004-144838).
A polarizing film having an absorption axis oblique to the width direction, which is obtained by such a manufacturing method, has less portions to be disposed at the time of punching and the rate of utilization thereof is high. However, in a conventional oblique stretching method, it is difficult to produce a thin (e.g., a thickness of 10 μm) polarizing film since the film tends to break in stretching.
On the other hand, there is a manufacturing method of a polarizing film different from the film stretching method, in which a liquid crystal compound is applied onto a support film in a thin film form and the liquid crystal compound is oriented to turn the thin film into a polarizing film.
In reference to FIG. 2, this manufacturing method will be described. A plurality of lyotropic liquid crystal compounds 31 are stacked in a solution with their absorption axes (major axes of molecules) 32 directed parallel to one another to form column-shaped aggregates 33.
The column-shaped aggregates 33 in a solution have the property of lining parallel to a direction 36 of orientation treatment of the support film 35 when a solution containing a lyotropic liquid crystal compound is applied onto the support film 35 in a thin film form. Therefore, an orientation direction 37 of the column-shaped aggregate 33 is parallel to the direction 36 of orientation treatment. Since the direction 36 of orientation treatment of the support film 35 is generally a longitudinal direction 38, the orientation direction 37 of the column-shaped aggregates 33 is the longitudinal direction 38 of the support film 35.
In this case, since the absorption axis 32 (major axis of a molecule) of the lyotropic liquid crystal compound 31 is perpendicular to the orientation direction 37, the absorption axis 32 is perpendicular to the longitudinal direction 38 of the support film 35. Therefore, the absorption axis 32 is parallel to a width direction 39 of the support film 35.
A polarizing film 40 is prepared by orienting many column-shaped aggregates 33 to be formed into a thin film. A composite film 30 is a laminate including the support film 35 and the polarizing film 40.
A thin (e.g., a thickness of 10 μm or less) polarizing film 40 can be easily obtained by using this manufacturing method. In the meantime, a conventional manufacturing method cannot give a polarizing film 40 in which the absorption axis 32 is oblique to the width direction 39 of the support film 35.